1. Field of the Invention
The present invention relates to an angular velocity sensing element which detects angular velocity of an object.
2. Description of the Related Art
Angular velocity sensing elements have been utilized in the technology of autonomously controlling attitude such as of boats, airplanes and rockets. Recently, use of such angular velocity sensing elements has been extended to small electronic devices, such as car navigation systems, digital cameras, video cameras and cellular phones. With this trend, there has been a need for the angular velocity sensing elements to have smaller size and lower height (reduced thickness).
Oscillation arms of oscillation type angular velocity sensors have prevalently been fabricated by machining and molding piezoelectric materials. However, since the accuracy of machining naturally has a limitation, it has been difficult to meet the need of the smaller size and lower height in the sensors.
To realize angular velocity sensors of smaller size and lower height, Japanese Patent Laid-Open Publication No. 2003-227719, for example, suggests a technique for finely processing a semiconductor substrate made such as of single crystal silicon to form oscillation arms.
Angular velocity sensors in general have a space around oscillation arms (drive arms and sensor arms) to ensure the oscillation range thereof. However, being applied with an unexpectedly violent shock, an angular velocity sensing element having such very small oscillation arms formed of a semiconductor material, may be applied with a stress exceeding the breaking stress of each of the oscillation arms, being induced by the excessively large oscillation of the oscillation arms. In particular, the stress may impart an unexpected impulsive force to each oscillation arm. In this case, the stress, which is quite difficult to be mitigated in a short time, may partly break or may sometimes rupture (snap off) the oscillation arms. Under such circumstances, what is concerned is that the intrinsic function or performance as an angular velocity sensor may be lost.
The present invention has been made in light of the circumstances described above, and has as its object to provide an angular velocity sensing element which is able to effectively prevent damage and breakage that will be caused on the oscillation arms, being induced by an excessively large shock applied to the oscillation arms.